We are investigating the consequences of mitogen mediated signals to T cells by isolating and characterizing genes that constitute the immediate early transcriptional response to these events. We have isolated over 60 novel cDNA clones that represent mRNA species induced by PHA and PMA in human peripheral blood T Cells. A subset of inducible genes (including two putative transcription factors) are constitutively expressed at high levels in T cells infected with HTLV-I, and also following transfection of T cells with HTLV-I-derived DNA encoding the overlapping reading frames of p42tax and p27rex. Such abnormally expressed genes may play a role in the deregulated growth of adult T cell leukemia, a cancer that shows a 100% infection rate with HTLV-I. The mechanism of p42tax and p27rex action that leads to over-expression is being examined.